The present invention relates to machine vision vehicle wheel alignment systems, and in particular to machine vision vehicle wheel alignment systems configured with imaging sensor systems which are mounted to movable vehicle support structures, enabling adjustments to the fields of view of the imaging sensor arrays for accommodating changes in the elevation of a vehicle supported by an adjustable vehicle lift structure.
Machine-vision vehicle wheel alignment systems typically use one or more imaging sensor arrays mounted away from a vehicle to obtain images of wheel-mounted alignment targets or other identifiable features associated with a vehicle. If utilized, the alignment targets may incorporate accurately reproduced patterns that have known control features, as set forth in U.S. Pat. No. 6,064,750 herein incorporated by reference. The alignment system may then use these images to calculate some or all of the six degrees of freedom (6-DOF) components for the alignment targets or identifiable features in the images. The 6-DOF components consisting of positional data (X, Y, and Z coordinates) and rotational data (rotation about the X, Y, and Z axis), which are otherwise known collectively as pose, and individually as pose components. Using some or all of the calculated six degrees of freedom components, or pose information, various vehicle wheel alignment measurements may be determined using known mathematical techniques. The precision of the 6-DOF components is limited by how accurately identifiable features of interest can be located in the image of the wheel assembly 100.
Some machine-vision wheel alignment systems do not use a predefined alignment target, but rather identify either random or selected identifiable features on the surfaces of the wheel or tire of a wheel assembly, such as projected light stripes or the circular wheel rim, and may use positional changes and/or the distortions of the feature geometry to determine some or all of the pose components for the wheel or wheel assembly, such as shown in U.S. Pat. No. 6,894,771 to Dorrance et al. herein incorporated by reference.
During a vehicle wheel alignment service procedure, it is common for a vehicle undergoing the service procedure to be positioned on an vehicle lift system such as shown in FIG. 1 to enable a technician to raise and lower the vehicle, as is required to access various components on the underside of the vehicle. A wide variety of vehicle lift systems are known. One type of vehicle lift system provides a pair of vertically adjustable runways on which the vehicle wheels are disposed. The runways may be either independent of each other, or coupled together with a connecting structure. Examples of vehicle lift systems employing two vertically adjustable runways include the model RX scissor lift rack, the model L421 Four-Post lift rack, and the RM parallelogram lift rack, each manufactured and sold by Hunter Engineering Co. of Bridgeton, Mo.
Typically, each runway in a vehicle lift system is provided with one or more actuating mechanisms, such as a hydraulic cylinder or screw drive, which is controlled from a common location to regulate the vertical elevation of the individual runways. For safety reasons, the control system which regulates the actuating mechanisms is generally configured to maintain each runway in substantially the same horizontal plane during changes in elevation. An exemplary lift control system is shown in U.S. Pat. No. 6,189,432 to Colarelli et al. herein incorporated by reference. Additionally, a mechanism is commonly provided to “lock” the runways at one or more predetermined heights during elevation or when the runways are stationary, preventing collapse of the vehicle lift system in the event of a failure in one or more of the actuating mechanisms.
When a vehicle is disposed on a vehicle lift system, it is preferred that the imaging sensor arrays associated with the alignment system be connected to a suitable elevating or orientating mechanism so that the alignment targets, vehicle wheel assemblies, or other vehicle features, remain within the fields of view of the imaging sensor arrays over the entire range of motion of the vehicle lift rack. Automated or manual elevating or orientating mechanisms may be utilized, such as described in U.S. Pat. No. 6,298,284 to Burns, Jr. et al. herein incorporated by reference. These may include hydraulic or pneumatic post systems, jack screws with motors, rack and pinion systems, and the like.
When components of the vehicle wheel alignment system such as the imaging sensor arrays are physically moved, either through changes in elevation or changes in orientation, established or identified relationships between the components can change. To maintain the degree of accuracy necessary for determining vehicle wheel alignment angles from the images obtained by the imaging sensor arrays, these changes must be identified and compensated for by the vehicle wheel alignment system. Accordingly, it would be advantageous to provide a method by which changes in the physical relationships between individual components of the vehicle wheel alignment system, such as multiple imaging sensor arrays, can be identified and compensated for, following a change in the physical location or orientation (pose) of the individual components of the vehicle wheel alignment system.